In the course of producing oil and gas wells typically a well packer along with completion and production equipment are run into cased wellbore. Upon reaching a predetermined depth the packer is set to the casing. A well packer may accommodate several tubular strings passing through the packer although two production tubular strings passing through a single packer is the most common due to wellbore diameter restrictions.
In many instances it may be desirable to be able to produce many different formation zones independently such as in multi-lateral wellbores or when the various formation zones have differing mechanical or chemical properties. In some instances each zone may require a separate production tubular or a separate control line. When multiple control lines or production tubulars are required to pass through a packer an at least dual zone packer may be required.
The purpose of a dual zone packer is to seal the wellbore against fluid or gas flow at the location of the packer while allowing the production tubulars or control lines to pass through. The packer is provided with slips having camming surfaces which, when activated, cooperate with complimentary opposed wedging surfaces to radially extend to and grip the wellbore casing. The packer also has an annular resilient seal, usually an elastomer, that is typically radially expanded to seal against the casing. Both the resilient seal and the camming surfaces that extend the slips are usually activated by a longitudinal compression of the packer. The longitudinal compression may be effected by mechanical or hydraulic means. When a dual zone packer is run into the wellbore it is usually retained in the unset position, typically by a shear pin or a c-ring.
Conventional dual string packers incorporate at least a pair of tubular mandrels on which a packing seal element and slip assembly are mounted. Typically the dual bore packer is prepared for setting by closing one of the mandrels to fluid flow. The fluid flow may be closed by using a ball, plug, dart, or any other device that may form a seal to block the particular tubular.
The resilient packer and the slip assembly are typically radially extended by a hydraulic piston that applies longitudinal compressive force in response to hydraulic pressure in the blocked mandrel. Setting forces are applied to the annular seal elements and the anchor by a setting cylinder mounted to the packer mandrel.
In certain instances it may be necessary to release the dual string packer in order to remove it from the wellbore. In order to facilitate easy removal of the packer from the wellbore certain features must be incorporated into the dual string packer as it is constructed. Typically the packer is constructed so that tension may be applied from the surface through one of the tubular mandrels to a shear assembly in the body of the packer. The tubular mandrel used to release the tension in the tool is typically referred to as the long side of the dual string packer. When enough tension is applied to the shear assembly from the surface to overcome the shear assembly's internal resistance and shears the relevant portions of the assembly the longitudinal compression applied to radially extend the slips and the resilient seal is released. The slips and the resilient seal no longer lock and seal the dual string packer to the casing and the dual string packer may be removed to the surface.
It is sometimes necessary to use one particular bore and at other times it is necessary to use the other bore as the source of hydraulic pressure to set the slips and the resilient seal. However, because only the long side of the dual string packer can be used to remove the dual string packer from the well and because each mandrel bore may have different requirements due to equipment and other requirements of the well, the operator is not usually able to easily reverse the orientation of the dual string packer prior to its deployment. It is usually necessary to reconfigure the internal portions of the dual string packer.
Typically, one of the tubing mandrels has a port built into it so that a flow path is created by the particular mandrel and the internal shifting chamber, while the other tubing mandrel has the necessary shear pins and other components to release the slips and seals when necessary. Since the through tubing mandrels pass through and are attached to the internal components of the dual string packer, a complete top to bottom rebuild of the dual string packer, usually on the rig floor, is called for in order to reconfigure the internal portions of the dual string packer. Such a rebuild takes valuable rig time and leads to possible contamination and potential failure of the tool when the dual string packer is deployed downhole.